Method and apparatus for x-ray analysis of particle size (XAPS)

ABSTRACT

The apparatus comprises an X-ray source ( 112 ), a monochromator ( 118 ), a goniometer ( 170 ), a position sensitive detector ( 150 ), a mechanism to rock or rotate the sample or the X-ray source and computer means ( 160 ) for interpreting the data obtained at the position sensitive detector. The method of the present invention includes the steps of generating an X-ray; narrowing the wavelength of the X-ray beam; allowing the particles to diffract the beam; detecting the diffracted beam with a position sensitive detector, collecting the diffraction data from individual particles; rocking or rotating the specimen or the X-ray source for successive times to cover the angular range of reflection of the particles; compilation of the diffraction data in the computer memory to construct the intensity profile for the individual particles; and interpreting the data to determine particle size and particle size distribution.

This application is a U.S. National Phase Application under 35 U.S.C. §371 of PCT Application Ser. No. PCT/US99/10723 filed May 14, 1999, whichclaims the benefit of U.S. Provisional Application Ser. No. 60/085,548filed May 15, 1998. The entire disclosures each of these applications isexpressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method and apparatus forx-ray analysis of particle size, XAPS for short, and more specificallyto a method and apparatus for determining particle size and particlesize distribution of crystalline particles comprising powders,suspensions or solids non-intrusively without the need to extractorseparate the particles from the other ingredients of the materials.

2. Related Art

The overwhelming majority of materials handled by industry, such asmining, chemicals, construction, agriculture and waste products, are inparticle or “powder” form. Many technologically important materials suchas ceramics, metals, composites, solid propellants, catalysts, magnetsand high-T_(C) superconductors all constitute particles or “grains” andare manufactured by consolidation of powders. Particle size is onedominant parameter in all these industrial products that dictates theirproperties and performance. Determination and control of particlecharacteristics, especially the particle size distribution, areessential for product quality control and performance.

Various methods have been developed in the past to determine theparticle size distribution in powders. These range from sieveelimination to laser scattering. Each one of these techniques has itsunique advantage and limitations.

The early techniques for characterizing fine particles depended heavilyon sieves, elutriators and microscopes. These techniques are timeconsuming and do not lend themselves to fast and practical measurements.In the period from the mid-1950's to the mid-1970's the methodology offine particle characterization improved rapidly with the introduction ofthe instruments as the Coulter Counter, other resista-zone counters andimage analyzers. Since mid-seventies the fine particle characterizationstudies have expanded substantially and many new techniques andinstrumentation have been developed. The highlights of this era includeholography for characterization of particles in mist and suspensionsystems; laser Doppler velocimetry (laser-photon correlationspectroscopy) for characterization of particles in aerosols and Brownianmotion; eriometry (light/laser diffraction) for evaluating fine particlepopulations based upon group diffraction patterns; signature-waveformcharacterization of scattered light for fine particle analysis; fractaldescription of fine particle profiles; and a new generation of imageanalyzers with powerful digitization and computer routines for fineparticle size and shape analysis.

Most of the recent techniques for particle size determination are basedon indirect measurements such as the optical properties of particlesobtained from scattering, diffraction, etc., of light or laser directedat the particle surface, or the disturbance of a homogeneous electricalfield by a passing particle. If an irregular shaped particle is measuredusing these physical properties, the “size”of this particle will differand depend on the particular property chosen. In these techniques,particle size is described by its so-called equivalent diameter, thediameter of a sphere, which yields the same response when analyzing acertain property as the irregularly shaped particle. For these reasonssignificant differences are found in the particle size distributionresults obtained by different commercially available instruments. Formeasurement of particle size in loose powders the scanning electronmicroscope (SEM) is a very useful tool because of its superiordepth-of-focus compared to optical microscopes. However, use of SEM isextremely time consuming in order to obtain statistically significantmeasurements. It also needs to operate under vacuum and is not amenablefor on-line applications.

On the other hand, none of the current particle-size analysis techniquesis applicable to multi-particle mixed solid materials, except formicroscopy in certain cases. Microscopy, however, requires destructivesectioning of the solids followed by tedious polishing and etchingprocedures. These procedures are difficult and time consuming, andsometimes unsuccessful for many ceramics, intermetallics, composites,energetics, and some metals. Particle size analysis of fillers inviscous suspensions (uncured) where the particles are encapsulated isyet another area, which is not feasible even with microscopy.

Analysis of particles in some of the suspensions and solids by thesetechniques might be feasible only after their constituents are separatedeffectively. One such technique involves the separation of particles,e.g. separation of solid filler particles from a suspension by heatingin an oven to pyrolyze and eliminate the viscous phase. Thereafter, theremaining particulate can be characterized by the known methods. Suchintrusive approaches, however, are usually ineffective and expensive.

All the methods mentioned so far, including the early methods, do notprovide information on the constitution of the fine particles, i.e.,when the fine particles contain more than one material orphase-polymorph, they are not differentiated by these techniques.Scanning electron microscopy (SEM) combined with energy dispersive x-rayfluorescence analysis (EDX) can differentiate compositional differencesbetween the particles in a mixed material. However, SEM with EDX isapplicable in general only if the components contain different andcontrasting elements that are heavier than oxygen and are not affectedby the vacuum. The EDX technique is also limited to submicron thicksurface layers and prone to errors due to surface films. Use of SEM withEDX is time consuming and is not amenable for on-line applications.

X-ray diffraction methods can be applied to determine the size ofparticles in some special cases. Early work has been done with Debye andback-reflection cameras. In these x-ray diffraction techniques particlesor grains of a polycrystalline material are irradiated with a collimatedbeam and diffraction takes place in the coherently reflecting planes ofthe particles. When large numbers of particles are irradiated under theincident beam, their diffraction spots overlap and form continuousdiffraction lines on appropriate Debye rings. Continuity of the ringsbreakdown and individual diffraction spots are resolved if the number ofdiffraction particles is reduced. However, the number of diffractingparticles is reduced and diffraction spots from individual particles areresolved only if the particle size is very large. Furthermore, thesex-ray techniques are very tedious and cannot be applied routinely.

Previous efforts in this area include:

Mack, U.S. Pat. No. 3,148,275 discloses a x-ray technique that is notfor particle size analysis. Rather, it relates to a special sampleholder to hold a curved specimen to improve wide-angle x-raydiffractometer (WAXRD).

Goebel, U.S. Pat. No. 4,144,450 does not disclose a particle sizeanalyzer, but rather relates to a wide-angle x-ray powder diffractometerequipped with a horizontal linear position sensitive proportionalcounter (PSPC) for simultaneous data collection from a range of 2θangles, on the equatorial diffraction plane. This is a regular WAXRDtechnique with a horizontal linear position-sensitive detector (PSD).This is not a particle size analyzer.

Ladell, U.S. Pat. No. 4,199,678 does not disclose a particle sizeanalyzer. Rather, it relates to a modified WAXRD for texture (preferredorientation) analysis with a point detector.

Rinik. et al., U.S. Pat. No. 4,649,556 discloses an indirect method toget information on the “average” particle size by making use of thevariation of diffracted intensity with WAXRD 2θ angle using a pointdetector. It does not obtain direct information on the particle size andcannot do measurements on individual particles to get particle sizedistribution.

Cocks. et al., U.S. Pat. No. 4,821,301 discloses a technique forglancing-angle x-ray-absorbance chemical analyses of thin (1000 Å)films. It does not relate to particle size analysis.

Moulai, U.S. Pat. No. 5,128,976 does not disclose a particle sizeanalyzer. Rather, it relates to an oscillation radiographer with a pointdetector. It is based on absorption contrast and uses a x-ray film torecord it. It does not use any of the beam path on the detector systemnor the type of data analysis that the present invention (XAPS) uses.

Goebel, U.S. Pat. No. 5,373,544 does not disclose a particle sizeanalyzer. Rather, it relates to an optimized WAXRD designed for thecapillary samples. It utilizes a curved mirror to focus the primaryx-ray beam and a mobile horizontal linear position sensitiveproportional counter with a radial collimator for simultaneous datacollection from a range of 2θ angles on the equatorial diffractionplane.

Carpenter, U.S. Pat. No. 5,418,828 does not disclose a particle sizeanalyzer like the present invention disclosed here, where large numberof particles, typically 0.51 μm to 300μm in size, can quantitatively beanalyzed simultaneously. This technique, rather, is meant for particleimaging for particles 1-2 mm in diameter or larger and generally willnot work for powders with smaller particle sizes. It uses a linearposition sensitive detector in horizontal configuration as opposed to avertical configuration of the present invention (XAPS). It uses thediffraction information by scanning to construct a low resolution“image” of a very large particle at one angular setting. In the presentinvention, diffraction information is obtained from rocking theparticles to get the total integrated intensity, which corresponds tototal volume/size of the particles, and it is the “integrated intensity”not the “image” that is utilized for particle size analysis.

Hautman, U.S. Pat. No. 5,446,777 discloses WAXRD with a horizontallinear position-sensitive detector that is designed to carry outlocation—specific WAXRD measurements on a give sample. It does notrelate to a particle size analyzer.

Yazici, et al., “Defect Structure Analysis of Polycrystalline Materialsby Computer-Controlled Double-Crystal Diffractometer withPosition-Sensitive Detector,” J. Appl. Cryst. (1983), discloses acomputerized double-crystal diffractometer and a position-sensitivedetector which analyzes defects in solid specimens.

None of these previous efforts, taken alone or in combination, teach orsuggest all of the elements of the present invention, nor do theydisclose the advantages of the present invention.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a method andapparatus for detennining particle size and particle size distributionof crystalline particles in powders, suspensions and solidsnon-intrusively without the need to extractor separate the particlesfrom the rest of the material.

It is another object of the present invention to provide a method andapparatus for determining the particle size at rates near real time foron-line process/product quality control applications in variousmanufacturing operations.

It is another object of the present invention to provide method andapparatus, which can determine particle size distribution of the solidingredients of formulations involving a plurality of different types ofcrystalline particles.

It is another object of the present invention to provide a method andapparatus, which can determine particle size distribution of particlesin more than one phase or polyrnorph.

It is another object of the present invention to provide a method andapparatus for differentiating between different components of acomposite or mixture in determining particle size distribution.

It is another object of the present invention to provide an apparatusfor determining the particle size distribution, which includes an x-raysource, a monochromator, a position sensitive detector and computermeans for determining particle size distribution.

It is still even another object of the present invention to provide amethod and apparatus for determining particle size distribution whichrocks a specimen or the x-ray source through the angular range ofreflection of the particles at Debye arc or portion thereof.

These and other objectives are achieved by the apparatus of the presentinvention, which comprises a x-ray source, a monochromator, agoniometer, a position sensitive detector and computer means forinterpreting the data obtained at the position sensitive detector. Themethod of the present invention includes the steps of generating anx-ray; narrowing the wavelength of the x-ray by means of amonochromator; placing a specimen in the path of the x-ray beam;allowing the particles to diffract the beam; detecting the diffractedbeam with a position sensitive detector; collecting the diffraction datafrom individual particles; rocking or rotating the specimen or the x-raysource for successive times to cover the angular range of reflection ofthe particles; compilation of the diffraction data in the computermemory to construct the intensity profile for individual particles; andinterpreting the data to determine particle size and distribution ofcrystalline particles.

By the method and apparatus of the present invention, particle size andparticle size distribution of crystalline particles in powders,suspensions and solids can be determined upon collection of samples froma process and characterization off-line at another location with theapparatus and method of the present invention, or on-line with theprocess using the apparatus and the method of the present invention.Importantly, the present invention allows for these determinations to bemade in situ, without the need for separating the particles, andsufficiently fast so that the generated data can be used in a processcontrol algorithm for quality and process control.

BRIEF DESCRIPTION OF THE DRAWINGS

Other important objects and features of the invention will be apparentfrom the following Detailed Description of the Invention taken inconnection with the accompanying drawings in which:

FIG. 1 is a schematic view of the present invention, X-ray Analyzer forParticle Size (XAPS), equipped with a linear position-sensitive detectorpositioned perpendicular to the equatorial diffraction plane and arocking multiparticle specimen or x-ray beam.

FIG. 2 is a graph of intensity versus azimuthal position ψ on a Debyearc obtained by the X-ray Analyzer for Particle Size (XAPS)configuration in FIG. 1.

FIG. 3 is a schematic view of the present invention, X-ray Analyzer forParticle Size (XAPS), equipped with a position-sensitive area detectorfor simultaneous analysis of multiple Debye arcs from different latticeplanes and multiple components/phases/polymorphs in a mixed compositematerial.

FIG. 4 is a graph of intensity versus azimuthal position ψ on two Debyearcs versus the angular position θ obtained by the X-ray Analyzer forParticle Size (XAPS) configuration in FIG. 3.

FIG. 5 is a graph of a typical X-ray Analyzer for Particle Size (XAPS)data for a single particle.

FIG. 6(A)-6(C) are flow charts showing the basic steps of the twocomputer programs used in connection with the invention, for datacollection and analysis.

FIG. 7 is a graph of absorption correction factors for sphericalaluminum particles and Cu K-α radiation versus the particle size.

FIG. 8 is a block diagram of the apparatus used in this invention.

FIG. 9 is a block diagram of a modified apparatus for performing thepresent invention in real or near-real time, as part of the productionprocess.

FIGS. 10a, 10 b, and 10 c are photomicrographs of the (a) “First,” (b)“Second” and (c) “Third” samples of the atomized aluminum powdersobtained by scanning electron microscope (SEM) at 500×magnification.

FIGS. 11a and 11 b are graphs of the “First” sample of atomized aluminumpowder. FIG. 11a contains the results of scanning electron microscopy(SEM) measurements, Frequency (number percent) vs. Particle size(microns), and FIG. 11b reports the results of X-ray Analyzer forParticle Size (XAPS) measurements, Frequency (number percent) vs.Intensity (photons per second).

FIGS. 12a and 12 b are graphs of the “Second” sample of atomizedaluminum powder. FIG. 12a contains the results of scanning electronmicroscopy (SEM) measurements, Frequency (number percent) vs. Particlesize (microns), and FIG. 12b reports the results of X-ray Analyzer forParticle Size (XAPS) measurements, Frequency (number percent) vs.Intensity (photons per second).

FIG. 13 is calibration curve for conversion of X-ray Analyzer forParticle Size (XAPS) intensity values obtained from aluminum particlesto X-ray Analyzer for Particle Size (XAPS) particle size values.

FIGS. 14a and 14 b are particle size distribution of the “Third” sampleof atomized aluminum powder. FIG. 14a contains the results of scanningelectron microscopy (SEM) measurements, Frequency (number percent) vs.Particle size (microns), and FIG. 14b reports the results of X-rayAnalyzer for Particle Size (XAPS) measurements, Frequency (numberpercent) vs. Particle size (microns).

FIGS. 15a and 15 b are SEM photomicrographs of HNIW powders. FIG. 15a isa SEM photomicrograph of “fine” HNIW powders at 2000× magnification andFIG. 15b is a SEM photomicrograph of “coarse” HNIW powders at300×magnification.

FIG. 16 is a graph of particle size distribution of the “fine” and“coarse” HNIW powders shown in FIGS. 15a and 15 b, as measured by theX-Ray Analyzer for Particles (XAPS), frequency (number percent) versesparticle size (microns).

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a novel method and apparatus that caneffectively measure the “true” size of individual crystalline particles,with the diffraction information that is directly proportional toparticle mass, and determine the particle size distributioncharacteristics in loose powders, suspensions, and solids. The techniquecan also differentiate the particles of the multiple ingredients in agiven mixed state and quantitatively measure the particle sizedistribution and the relative volume fraction and phase or polymorph ofeach component. The method and apparatus of the present invention can beused to determine the particle size of individual crystalline andsemi-crystalline particles including powders, grains and whiskers, inloose powders, particle-filled viscous suspensions and multi-particlesolid materials. The present invention is a non-invasive technique thatrequires minimum sample preparation. Measurements can be carried out inambient atmosphere without the need for the application of vacuum,carrier fluids or other medium. Each measurement may take only a fewminutes of time or less depending on the sample material and may even beperformed “on-line” at production facilities.

Referring to FIG. 1, it can be seen that a monochromatic x-ray beam 20is directed at a specimen 30 and impinges on particles comprising thespecimen which causes a diffraction of the x-ray beam indicated at 40 a,40 b, 40 c, and 40 d emanating from particles a, b, c, d on thespecimen. These diffracted beams 40 a-40 d are picked up by positionsensitive detector 50 a, through entry slit 52. The azimuthal position ψon the Debye arc, which is made to coincide with the length of the PSD,is identified and the intensity I is measured as graphically shown inFIG. 2. A computer means is utilized to interpret the data from theposition sensitive detector 50 a.

Although the XAPS unit utilizes a highly parallel crystalmonochromatization where the monochromator can be symmetrically orasymmetrically cut, flat or curved, single, two-parallel or channel-cutcrystals, other means of obtaining highly parallel monochromatic beamare also considered. For example, combined use of filters, curvedmirrors, tapered capillaries or parallel and monochromatic sources suchas accelerators, plasmadischarge units or a synchrotron source can allbe used.

This setup for the present invention is carried out in a high precisionθ—θ diffractometer and includes a x-ray source, a θ—θ goniometer forrotating the sample or the x-ray source, and a detector such as aposition sensitive detector 50 a. Additionally, a monochromator, such asa crystal-monochromator and various slits, collimators and capillariesmay be used to obtain a highly parallel monochromatic x-ray beam 20having very narrow wavelength. X-ray film, a position sensitivedetector, or a CCD camera can be used to detect and differentiate thediffraction of the monochromatic x-ray beam from the individualparticles of the specimen.

The present invention is based on double-crystal diffractometry method,where individual particles are regarded as the second or test crystal ofthe double crystal diffractometer. During measurements, the particulatesample or the x-ray source may be oscillated, rotated or rocked for asum of several tens of minutes of arc about the Bragg angle, while beingirradiated by a crystal or otherwise monochromated parallel x-ray beam.Several particles (or grains) in the sample will be in Bragg reflectingpositions which result in individual microscopic diffraction spots alongthe appropriate Debye arc. These spots are detected by aposition-sensitive detector (PSD) either linear 50 a and orientedparallel to the Debye arc or a two-dimensional 50 b PSD, or a CCD cameraor a fiber-optic detector or an image plate or a film or any other twodimensional position sensitive detector system. These principles ofoperation of the XAPS method and the diffraction peaks obtained areschematically shown in FIGS. 1 and 2 for one dimensional detectors 50 a,and in FIGS. 3 and 4 for two dimensional detectors 50 b. The intensitydistribution of each diffraction spot of an individual particle and itslocation and distribution are then stored in a computer for subsequentnumerical analysis (see FIG. 5). The integrated intensity of anindividual diffraction spot is directly proportional to the volume andmass of the particular diffracting particle in the sample.

The primary x-ray beam 20 can be monochromatized in a number of wayslike diffraction from the planes of a flat or channel-cut crystal. Uponmonochromatization the resultant monochromatic beam has a very smallhorizontal convergence and is nearly parallel, while the verticaldivergence of the beam is controlled by a slit, collimator or capillarysystems. In one embodiment of the invention the sample underinvestigation is mounted on a two-dimensional microscope stage whichenables precise selection of the region of interest. The axis of thesample holder is rotated by a stepping motor for orienting along anappropriate angle. Various detectors including a one-dimensionalposition-sensitive detector, which is located parallel to the Debye arc,a two-dimensional position sensitive detectors a CCD camera or afiber-optic detector or an image plate or film or any othertwo-dimensional position sensitive detection system can be used. Atypical source, i.e., 0.5-3 kW diffraction tube with a Cu target may beused as the x-ray source, however, other sources including rotatinganode sources using Cr, Mo or other targets that generate softer orharder x-rays are useable. Each measurement may take up to a fewminutes. The speed and resolution can also be enhanced, if necessary.

The present invention can typically analyze particles ranging in sizefrom 0.5 μm to 300 μm in diameter, without altering its x-ray optics.These limits however, can be expanded by making appropriate changes inthe x-ray optics. For example, by use of a microfocus x-ray sourceand/or a tapered capillary to focus the incoming beam, the lower limitof the particle size analysis can be further lowered from 0.5 μm. And,conversely, by use of a harder (shorter wavelength) x-ray beam andcalibrated collimator/slit systems the upper limit in the particle sizeanalysis can be further increased from 300 μm to several millimeters.

As an additional embodiment of the invention, the vertical andhorizontal divergence of the monochromatic beam can be adjusted, forexample, by adjustable slits, for vertical and by use of asymmetriccrystals, for horizontal divergence, and through such alterations of thex-ray optics the width of the beam divergence can be tuned with that ofthe angular-range-of-reflection of the given particles, and this way theparticle size can also be determined from a single exposure withoutrocking the sample or the beam.

Flow charts of programs used in the present invention are shown in FIGS.6(A)-6(C). The programs are used to determine the particlesize/intensity/distribution and utilize algorithms for datainterpretation, background correction, peak and integrated intensitydetermination and statistical analysis and graphics for the deduction ofparticle size distribution parameters. These include: 1) a program (XAPSDATA COLLECT), FIG. 6A, that has been developed for automation of themoving parts in the XAPS apparatus and for data acquisition; and 2) aprogram (XAPS DATANALYST), FIGS. 6(B) and 6(C) for data analysis todetermine the particle size/intensity/distribution, including a set ofalgorithms for data interpolation, background correction, peak andintegrated intensity determination and statistical analysis and graphicsfor the deduction of particle size and microstrain distributionparameters.

In one embodiment the x-ray intensity spectra of multiple particlereflections are collected and displayed, as shown schematically in FIGS.2 and 4, by a multichannel analyzer (MCA) and a computer. Subsequently,the spectra from individual particles are stored in the computer asshown in FIG. 5 for further analysis. A large particle population canreadily be analyzed at each region of interest by taking multipleexposures at the Bragg angle. Also, the entire sample surface can beanalyzed by moving the sample with a microstage relative to the incidentbeam.

If no control experiments are possible the intensity values have to becorrected for absorption. The integrated intensity of the diffractionfrom an individual particle is directly proportional to the volume ofthe particle. The intensity is given by:

I=I ₀ K/r ² |F| ² p(l+cos²2θ)/(sin²θcosθ)A(θ)e ^(−2M)  (1)

Where, I: diffracted beam intensity, I₀: incident beam intensity, K:constant, r: distance from the diffraction site, F: structure factor(material dependent), p: multiplicity factor (material dependent), θ:Bragg angle (material and x-ray wavelength dependent), A (θ): absorptionfactor (material, x-ray wavelength and (particle) size and shapedependent), e^(−2M): temperature factor. The absorption factor is givenby:

A(θ)=A(hkl)=1/Vexp{−μ(p+q)}dV=1/A*  (2)

Where, h, k, l: Miller indices, V: volume (of the particle), μ: linearabsorption coefficient (material and x-ray wavelength dependent), p andq: the lengths of the paths of the incident and reflected beams in thematerial (θ and particle size and shape dependent), A*: correctionfactor for absorption to get the “true” intensity.

According to equations 1 and 2, the relationship between the intensityand the particle mass/volume deviates from linearity depending on theabsorption characteristics of the monochromatic x-rays for the givenmaterial that is being tested. A correction function has to be appliedin order to obtain the “true” intensity and the “true” particle volumefrom the intensity values. For a multitude of materials the correctionfactors, A*, are given in a normalized format in International Tablesfor X-ray Crystallography. These calculations are possible for a fewregular particle shapes such as an ideal sphere or a cylinder. Suchcalculations were carried out for a spherical aluminum particles andCuKa radiation. The results of this work are shown in FIG. 7. However,majority of the powders contain particles with irregular shapes, and inorder to achieve high accuracy in the particle size versus intensitycorrelations, a one-time calibration measurement needs to be carriedout, preferably with scanning electron microscopy (SEM) for the particlesize of the same material.

The present invention is applicable to particles which are crystallineor highly amorphous particles and particles with excessive plasticdeformations cannot be analyzed by this method and apparatus.

A block diagram of the XAPS system of the present invention, foroff-line applications, is shown in FIG. 8 The x-ray source for thesystem could be a rotating anode or a sealed x-ray tube 112 with itshigh-voltage supply 110. These x-ray generators are available fromnumerous manufacturers. The ones currently utilized are a Rotaflexrotating anode system by Rigaku, Danvers, Mass., and a XRD-6 sealed-tubesystem by General Electric, Schenectady, N.Y.

A monochromator 118 and a θ—θ-ω goniometer 170 currently used is made byPicker model 3488L. Similar goniometer and monochromators are alsoavailable by Huber, Blake Industries, Scotch Plains, N.J. Currently aflat symmetric-cut Si(III) single crystal and an asymmetric-cut Si (III)crystal are used in the monochromator 118 to obtain a monochromaticparallel beam 120. This beam 120 is diffracted by particles in thesample 130 to create diffracted beam 140.

The Picker unit has been retrofitted with a stepping motor system forautomation: model M092-FC08 motor by Superior Electric, Bristol, Conn.,and a stepper control model DPH37 by Anaheim Automation, Anaheim, Calif.Sample rotation/rocking step of 0.1 minutes of arc about angles θ, ω, ismade possible with this system. For the off-line XAPS system shown inFIG. 8, only the sample 130 is rotated or rocked. The x-ray source 112and the position sensitive detector (PSD) 150 are held stationary.

There are two linear PSD 150 and related PSD electronics 152 systemsthat are used in the current invention. One PSD system is manufacturedby TEC, Knoxville, Tenn., Model 200-PD-01 detector and Model 200-DM-01signal processing electronics. The other PSD system is manufactured by MBraun, Garching, Germnany, Model PSD-50M and Model ASA-5 electronics.

The computer 160 used for automation of the goniometer 170, dataacquisition from the PSD electronics 152 and for data analysis, is anIBM-PC type computer 486 or better, available from numerousmanufacturers. For data acquisition, the signals from the PSDelectronics module 152 are captured by a multi-channel analyzer (MCA)PC-board installed in the PC. Currently, two MCA boards are beingutilized, both manufactured by EG&G Ortec, Oak Ridge, Tenn. The boardsare Model Trump-2K and Model Trump-8K-W3, respectively.

A block diagram of the XAPS system of the present invention for on-lineapplications is shown in FIG. 9. The on-line version is designed andbuilt for carrying out particle size distribution analysis in processingand manufacturing environments, on-site and on-line with the processingequipment 282 so that manufactured products such as powders,powder-binder suspensions or powder binder solid articles are analyzedimmediately for quality control. Currently, conveyor system 280 in FIG.9, Model 2100 by Donner, Hugo, Minn., is employed to bring the samplematerial to the correct position at the center of the x-ray unit 270 b.In this way, particle size distribution of particles found in thepowder, suspension or solid forms may be analyzed sequentially. Themeasurements are done intermittently where the conveyor is brought to ahalt for each sampling during XAPS measurements. The goniometer 270 bemployed for on-line analysis is a vertical theta-theta goniometer ModelD8 manufactured by Bruker, AXS, Madison, Wis. The goniometer has acircular opening 272 in the middle to accommodate the conveyor to passthrough, see 280 passing through 270 b in FIG. 9. The x-ray source 212 bin this version comprises a sealed-tube x-ray generator. In thetheta-theta optics, the x-ray source 212 b rotates/rocks with theta (θ)motion instead of the sample. The sample is not rotated, but heldstationary, in this on-line version of XAPS, making it possible todeliver and analyze samples in as-processed condition. The monochromator218 b includes a curved x-ray mirror for focusing and to obtain a higherx-ray intensity. The beam 220 is diffracted by particles in the sample230 to create a diffracted beam 240. The PSD system 250 and 252 is madeby M Braun as previously set forth.

The computer means 260 b used in the on-line version of XAPS is designedto handle additional tasks compared to the off-line version. In additionto the automation of the goniometer, data acquisition from PSD and dataanalysis, the computer means of the on-line version is able to donear-real time analysis by multi-tasking and also the on-line version iscapable of controlling the conveyor 280 motion and communicating withthe processing equipment 282 for feedback and quality control tasks.

In a further embodiment of the invention the x-ray unit can be made tomove at the same linear speed as the conveyor to allow the determinationof the particle size without interrupting the flow of the processstreams.

In yet another farther embodiment of the invention the x-ray unit can bekept fixed but the data acquisition system can be programmed to “follow”the moving particles on the conveyor to allow the determination of theparticle size without interrupting the flow of the process streams.

To demonstrate the present invention, particle size measurements werecarried out on three aluminum powders, which were processed bygas-atomization from melt, and all three constituted near-sphericalparticles. The average particle size of two of the powder grades werespecified by the manufacturer, Ampal, Inc., as 8 μm and 55 μm,respectively and were used as the calibration samples. The “Third”aluminum powder lot with an unknown particle size distribution was usedas test material.

A double-sided conductive carbon adhesive tape was used as the mountingmedium to hold the loose powder during the x-ray diffraction andscanning electron microscopy (SEM) measurements. Particles were spreadon the tape in a monolayer for stability and ease of SEM image analysis.

Control measurements of particle size distribution were carried out witha scanning electron microscope. The typical SEM photomicrographs of thethree atomized aluminum powders are shown in FIGS. 10a, 10 b, and 10 c.As shown in FIG. 10, all three powders exhibit nodular particles withrounded nearspherical features which are typical ofgas-atomization-from-melt powder processing. In this technique, thesecondary electron images of the particles were photographed at highmagnification and images were analyzed for particle size determination.An image analysis software was employed for these studies.

The results of the particle size distribution measurements of the“First”and “Second” aluminum powders are graphically shown in FIGS. 11and 12, respectively. In FIGS. 11 and 12 the results of both, (a) SEM,and, (b) the XAPS particle size distribution measurements are given forcomparison. The SEM results are given in frequency (percent of totalnumber of particles) versus particle size (microns). The XAPS resultsare given in frequency (percent of total particle number) versus x-raydiffraction intensity from individual particles (number of photon countsper second, cps). As can be seen in FIGS. 11 and 12, the frequencydistributions of the intensity values of the present invention are invery good agreement with the frequency distribution of the SEM particlesize values since intensity is directly related to particle mass andsize.

These results of the “First” and “Second” aluminum powders, i.e., themean, mode, maximum and minimum values and other statisticaldistribution characteristics (FIGS. 11 and 12) were utilized tocalibrate (or train) the XAPS technique for the particle sizedistribution analysis of the aluminum powders. Through this work acalibration curve for the intensity values was obtained, with respect tothe SEM particle size values. This calibration curve is given in FIG.13. By using this calibration curve the intensity values obtained fromanother aluminum powder, with unknown particle size distribution, wasconverted to particle size values, by carrying out the measurementsunder identical x-ray optics conditions.

This calibration procedure was put to test with the “Third” aluminumpowder sample. The results of this work, the particle size distributionof the “Third” sample measured by the present invention are given inFIG. 14a, where, the SEM results from the same sample are also shown forcomparison in FIG. 14a. As evident in FIG. 14, the particle sizedistribution values obtained by the present invention and SEM methodsare in very good agreement. Minor differences observed between the twomethods are within the expected experimental error of each technique.“Third” powder exhibits close to a bimodal particle size distribution asevident in the SEM photomicrograph in FIG. 10c. This near bimodalcharacteristics of the particle size distribution of the “Third” powderwas successfully determined by the present invention (see FIG. 14b). Theaverage particle size by number values obtained with the presentinvention and SEM methods were seven microns and five microns,respectively. These results are in very good agreement considering thatthe particle size distribution of this “Third” sample extends from 0.5μm to 40 μm.

The technique has been also applied to other materials. The results ofXAPS particle size distribution analysis of HNIW(hexanitro-hexaazaiso-wurtzitane) powders are shown in FIGS. 15a and 15b and 16. In these analysis “Fine” and “Course” HNIW powders wereanalyzed and similar calibration techniques, as with the aluminumpowders, were applied to determine the particle size distributions. Asshown in FIGS. 14a and 14 b, particles as small as 0.5μ were present inthe “Fine” HNIW powder, and in the “Coarse” HNIW powder particle sizedistribution approached a bimodal particle size distribution. Thesefeatures were captured successfully with the XAPS analysis (see FIG.16).

This demonstration is indicative of the ability of the technique of thepresent invention to capture changes in particle size distribution whichcan occur during crystallization, processing or heat treatment andsuggests its potential for use as an off-line or on-line quality controlmonitoring technique during manufacturing operations.

Every crystalline material generates characteristic diffraction peaks atdifferent Bragg angles. In a multi-phase polymorph or composite materialwhere two or more materials are mixed, particles from each materialgenerate diffraction spots at separate Debye arcs positioned at unique θangles. Particles with different crystal structures can be analyzed bythe present invention by: (1) either sequentially placing a positionsensitive linear detector (PSD) at the appropriate Debye arcs as shownin FIG. 1, or (2) simultaneously, by employing multiple linear PSD's, ora 2-dimensional PSD or a CCD camera, or a fiber-optic detector or animage plate or a film, or any other two-dimensional position sensitivedetection system 50 b, as shown in FIG. 3. By this technique of thepresent invention the particle size and relative particle volumefraction of multiple phases or polymorphs can be determined at a givenlocation in the mixture, such as shown in FIG. 4, where 40 a, 40 b, 40 cand 40 d versus 40 e, 40 f, 40 g, 40 h and 40 i could originate from twodifferent phases or components.

Having thus described the invention in detail, it is to be understoodthat the foregoing description is not intended to limit the spirit andscope thereof. What is desired to be protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method of determining individual particle sizeand particle size distribution of particles in crystalline powders,suspensions and solids comprising the steps of: generating an x-ray;narrowing the wavelength of said x-ray; placing a specimen in the pathof said narrowed wavelength x-ray; diffracting said narrowed wavelengthx-ray with said specimen; detecting said diffracted x-ray; determiningthe position of the diffracted x-ray; and determining individualparticle size and particle size distribution based on said position ofsaid diffracted x-ray.
 2. The method of claim 1 further comprising thestep of rocking or rotating the specimen or the x-ray for successivetimes; and determining the position of the successive diffracted x-rays.3. The method of claim 2 wherein said narrowing step employs amonochromator.
 4. The method of claim 2 wherein said position of saiddiffracted x-ray detects the particles or grains in said specimen attheir Bragg reflecting positions which have produced said diffractedx-ray along the appropriate Debye arc.
 5. The method of claim 4 furtherincluding the step of determining the intensity distribution of saiddiffracted x-ray.
 6. The method of claim 4 further including the stepsof collecting intensity distributions of said diffracted x-ray formultiple particles and integrating the intensity of each diffractedx-ray to provide an indication of the volume and mass of a particulardiffracting particle and determining the same for multiple particles toobtain the particle size distribution of the particle population in saidspecimen, and further, to differentiate the particles of mixedingredients and determine their concentration in the mixture.
 7. Amethod for determining individual particle size and particle sizedistribution of particles in crystalline powders, suspensions and solidscomprising the steps of: moving a sample into a testing position;generating an x-ray from an x-ray source at a first position; directingthe x-ray at the testing position to impinge on the sample; detectingdiffracted x-rays; moving the x-ray source to successive positions;directing the x-ray at the testing position to successively impinge onthe sample; detecting diffracted x-rays; and determining individualparticle size and particle size distribution based upon the detecteddiffracted x-rays.
 8. The method of claim 7 wherein said position ofsaid diffracted x-ray detects the particles or grains in said sample attheir Bragg reflecting positions which have produced said diffractedx-ray along the appropriate Debye arc.
 9. The method of claim 8 furtherincluding the step of determining the intensity distribution of saiddiffracted x-ray.
 10. The method of claim 9 further including the stepsof collecting intensity distributions of said diffracted x-ray formultiple particles and integrating the intensity of each diffractedx-ray to provide an indication of the volume and mass of a particulardiffracting particle in said sample.
 11. The method of claim 8 furthercomprising moving the x-ray source with the sample.
 12. A method ofdetermining particle size and particle size distribution of particles incrystalline powders, suspension and solids comprising the steps of:collecting data on x-rays diffracted from specimens; conditioning thecollected data; determining local maxima for the collected data;separating peaks; creating a three dimensional matrix of intensityversus azimuthal position versus rotational angle for the collectedpeak; calculating integrated peak intensities; and calculating particlesize and particle size distribution.
 13. An apparatus for determiningindividual particle size and particle size distribution of particles incrystalline powders, suspensions and solids comprising: means forgenerating an x-ray; means connected to said x-ray generating means forreceiving said x-ray and for generating an x-ray output which has anarrower wavelength than said generated x-ray; means for impinging saidnarrower wavelength x-ray on a specimen for producing a diffracted x-raybased on particle size and particle size distribution in said specimen;detecting and position determining means connected to receive saiddiffracted x-ray for detecting said diffracted x-ray and for determiningthe position of said diffracted x-ray; means connected to said specimenor said means for generating an x-ray for rocking or rotating saidspecimen or said x-ray generating means for successive impingements; andmeans connected to said detecting and position determining means formeasuring individual particle size and particle size distribution basedon said position of said diffracted x-ray.
 14. The apparatus of claim 13wherein said means for generating a narrower wavelength x-ray includes amonochromator.
 15. The apparatus of claim 13 wherein said detecting andposition determining means detects particles or grains in said specimenat their Bragg reflecting positions which have produced said diffractedx-ray along the appropriate Debye arc.
 16. The apparatus of claim 15further including means connected to said detecting and positiondetermining means for measuring the intensity distribution of saiddiffracted x-ray.
 17. The apparatus of claim 16 further including meansfor collecting intensity distributions of said diffracted x-ray formultiple particles; and means connected to said intensity distributioncollecting means for integrating the intensities of each diffractedx-ray for providing an indication of the volume and mass of a particulardiffracting particle in said specimen.
 18. An apparatus for analyzingindividual particle size in a specimen, the apparatus comprising: anx-ray source for generating an x-ray output signal; monochromator meanscoupled to the x-ray source for producing a monochromatic parallel x-raysignal for irradiating a specimen and producing output signalsindicative of particle characteristics of the specimen; means for movingsaid specimen in the path of said monochromatic parallel x-ray signal;position sensitive detector means for receiving said output signals fromthe specimen and generating output indications of the azimuthal andangular position of said output signals; and computer means connected toreceive said output indications for analyzing individual particle sizeand particle size distributions of the specimen.
 19. The apparatus ofclaim 18 wherein said position sensitive detector means detectsparticles or grains in said specimen at their Bragg reflecting positionswhich have produced said output signals along the appropriate Debye arc.20. The apparatus of claim 19 further including means connected to saidposition sensitive detector means for measuring the intensitydistribution of said output signals.
 21. The apparatus of claim 20further including means for collecting intensity distributions of saiddiffracted x-ray for multiple particles, and means connected to saidintensity distribution collecting means for integrating the intensitiesof each diffracted x-ray for providing an indication of the volume andmass of a particular diffracting particle in said specimen.
 22. Anapparatus for analyzing individual particle size in a product duringfabrication of the product, the apparatus comprising: conveyor means forsupporting and moving a product into position for measurement duringfabrication; x-ray generating means for irradiating said product forgenerating output radiation signals from said product; means for movingsaid x-ray generating means in a predetermined pattern for successiveintermittent irradiations; position sensitive detector means forreceiving said output radiation signals and for generating indicationsof the position sensitive detector means, said moving means and saidconveyor means for analyzing said output radiation signals, controllingthe position of said moving means and the operation of said conveyormeans; and means for determining individual particle size and particlesize distributions.
 23. The apparatus of claim 22 wherein said positionof said output radiation signals detects the particles or grains in saidproducts at their Bragg reflecting positions which have produced saiddiffracted x-ray along the appropriate Debye arc.
 24. The apparatus ofclaim 23 further including means for determining the intensitydistribution of said output radiation signals.
 25. The apparatus ofclaim 24 further including means for collecting intensity distributionsof said output radiation signals for multiple particles and integratingthe intensity of each output radiation signal to provide an indicationof the volume and mass of a particular diffracting particle.
 26. Theapparatus of claim 25, further comprising means for collecting anddetermining intensity distributions for multiple particles to obtain theparticle size distribution of the particle population in said products,and further, to differentiate the particles of mixed ingredients anddetermine their concentration in the mixture.